1.构造器调用

注意子类调用父类构造器和子类调用子类其他构造器

2.initPropertySources()方法扩展

AbstractApplicationContext#initPropertySources()扩展，子类重写方法即可。

3.customizeBeanFactory 定制BeanFactory

	protected void customizeBeanFactory(DefaultListableBeanFactory beanFactory) {if (this.allowBeanDefinitionOverriding != null) {beanFactory.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);}if (this.allowCircularReferences != null) {beanFactory.setAllowCircularReferences(this.allowCircularReferences);}}

4.loadBeanDefinitions(beanFactory)

读取bean配置信息